Exhaust gas analyzer

ABSTRACT

An SOF measuring system that can continuously measure SOF and a soot measuring system that can continuously measure soot are connected with an exhaust gas line. The soot measuring system comprises a diluter that selectively dilutes either one of the exhaust gas and standard gas whose hydrocarbon concentration is known with diluent gas and extrudes it. A dilution ratio adjusting device can adjust a dilution ratio of the diluter. A soot detector continuously detects soot in the exhaust gas or the standard gas diluted by the diluter. The SOF measuring system can be connected with the diluter so that an exhaust gas analyzer can measure the hydrocarbon concentration in the standard gas diluted by the diluter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/288,531,filed Nov. 29, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an exhaust gas analyzer used for continuouslymeasuring particulate matters (PM) included in exhaust gas of a dieselengine of, for example, a vehicle.

2. Background Art

Minute particulate matters (PM) that might cause an adverse effect onthe environment or human health are contained in exhaust gas of aninternal combustion engine such as a diesel engine, and soot and solubleorganic fraction (SOF) or the like are mixed in the particulate matters.

In order to improve the internal combustion engine so as to reduce theparticulate matters, it is necessary to measure the PM emissionsaccurately. According to a method for measuring exhaust gas that ispublicly specified by the requirement of current laws and regulations,it is specified that the PM is collected by a filter and the collectedPM is weighted on a microbalance.

However, since it is impossible for this method to collect thegenerating PM dynamically, there is a demand for a simple measurementinstrument that is capable of a real-time continuous PM measurement in astep of research and development of an internal combustion engine.Furthermore, recently since the PM emission is considerably decreasingdue to improvement of the internal combustion engine, a demand formeasuring a minute amount of PM emissions has been increasing inaddition to the continuous measurement.

Regarding SOF, a method has been developed that can continuously andaccurately measure concentration of liquefied or solidified particulatehydrocarbon (SOF) in exhaust gas at a certain reference temperature (47°C.±50° C.) by the use of a detector high-sensitive to hydrocarbon suchas a flame ionization detector (FID).

Regarding soot, the inventors have been developing a high-sensitive sootdetector that can perform continuous measurement by making use of adiffusion charge detecting method.

This kind of a soot detector requires that the exhaust gas be diluted toconcentration appropriate to the exhaust gas measurement because it ishigh sensitive, however, there are the following problems in dilutingthe exhaust gas.

First, it is required to grasp a dilution ratio in order to calculatethe concentration of soot in the original exhaust gas based on theconcentration of soot in the measured diluted exhaust gas.

However, in order to obtain the dilution ratio if the soot detector hasan arrangement wherein a flow of the exhaust gas prior to dilution and aflow of the exhaust gas after dilution are measured respectively by theuse of a venturi meter and the dilution ratio is calculated based on theflow ratios, the soot detector becomes large and costly.

Secondly, it is preferable that the dilution ratio by the diluter can bechanged with ease because the concentration of soot in the exhaust gasis affected to change by a variety or a state of the internal combustionengine.

However, if the exhaust gas as being sample gas or the diluent gas isforcefully fed or sucked by the use of, for example, a rotary pump inorder for dilution, a bad influence might be exerted upon sootmeasurement such that an unexpected portion is clogged with soot becausethe fluid path inside the pump is complicated. In addition, the rotarypump is not suitable for accurate soot measurement because of pulsationgenerating in the diluted exhaust gas.

On the contrary, an ejector that conducts liquid transfer by making useof an involute action of fluid blowing out due to bounded jet has asimple flow path and there is no pulsation generating. Then the ejectorcan be used as a diluter that is very preferable for this kind ofmeasurement.

However, generally it is considered that the ejector can not change adilution ratio arbitrarily (if a lot of diluent gas is flowed, pressurein a nozzle diffuser part decreases and the flow volume of the samplegas increases by just this much and consequently the dilution ratio doesnot change significantly), the ejector has a problem with this point.Conversely, the ejector is often used in a case that the dilution ratiois to be kept to some extent or in a case that the dilution ratio is notcared at all (for example, a pump).

As mentioned, the ejector has a merit that the flow path is simple andfree from pulsation, however, it is considered that it has a demeritthat the dilution ratio can not be adjusted easily when used as adiluter. As a result, it is difficult to use the ejector for not onlysoot measurement but also other use such as the dilution ratio or themixing ratio is required to be adjusted.

SUMMARY OF THE INVENTION

The present claimed invention intends to solve the above-mentionedproblems concerning dilution in measuring the exhaust gas, moreconcretely, desired objects are mainly (1) to make it possible to obtaina dilution ratio necessary for soot concentration measurement with asimple and low-cost arrangement by making use of the SOF measuringsystem with focusing attention on that both concentration of SOF andconcentration of soot are measured in measuring diluted particulatematters, (2) to provide an exhaust gas analyzer that can easily changeand adjust a dilution ratio in case of diluting the exhaust gasconducted at a time of soot measurement and to provide a superior mixingsystem that can be used broadly for diluting and mixing gas. It is notuntil the inventor of the present claimed invention found out that therewas an area where flow of sample gas almost never changed even thoughflow of the dilution gas was changed as a result of keen examinationthat the problem (2) is solved.

First, regarding the problem (1), an exhaust gas analyzer in accordancewith this present claimed invention comprises the following requirement.

I. An SOF measuring system that can continuously measure concentrationof SOF in exhaust gas and a soot measuring system that can continuouslymeasure concentration of soot in the exhaust gas are connected with anexhaust gas line through which a part or all of the exhaust gasdischarged from an internal combustion engine flows.II. The soot measuring system comprises

-   -   a) a diluter that selectively dilutes either one of the exhaust        gas and standard gas whose hydrocarbon concentration is known        with diluent gas and extrudes it,    -   b) a dilution ratio adjusting device that can adjust a dilution        ratio of the diluter, and    -   c) a soot detector that detects soot in the exhaust gas or the        standard gas diluted by the diluter.        III. The SOF measuring system can measure hydrocarbon        concentration in the standard gas diluted by the diluter with an        arrangement that the SOF measuring system can be connected with        the diluter, and the dilution ratio of the diluter at this state        can be calculated based on the hydrocarbon concentration in the        standard gas after dilution when the dilution ratio adjusting        device is operated by a certain amount.

In accordance with this arrangement, it is possible to obtain thedilution ratio of the diluter at a time of soot measurement by the useof the standard gas at a time prior to or after soot measurement and tocalculate the concentration of soot in the exhaust gas prior to dilutionbased on the obtained dilution ratio and the concentration of soot inthe diluted exhaust gas detected by the soot detector with anarrangement of a simple flow path wherein the piping is bifurcated fromthe diluter to be connected with the existing SOF measuring system, thepiping to connect the standard gas source is connected with the diluter,or the switch valves are arranged on the piping.

The diluter might be clogged with soot if a fluid path inside of thediluter has a complicated arrangement because soot flows in the diluter.In addition, if there is pulsation generating in the flow at a time ofdilution, the pulsation might be a cause of an error of measurement bythe soot detector. Then in order to make the diluter that is free frompulsation at a time of dilution with a simple arrangement, it ispreferable that the diluter comprises a narrow part whose flow pathdiameter is narrowed and a diffusible part whose flow path diameter isextended and that is serially arranged to the narrow part, the diluentgas is accelerated to be negative-pressured by passing the diluent gasthrough the narrow part and the diffusible part, and the exhaust gas orthe standard gas is sucked because the diluent gas is negative-pressuredso that the exhaust gas or the standard gas is mixed with the diluentgas. It would be further more preferable from a viewpoint of mixing if adiffusible part is serially arranged downstream of the narrow part.

As a concrete embodiment of the dilution ratio adjusting devicerepresented is a pressure regulator that adjusts pressure of the diluentgas introduced into the diluter.

As a soot detector that can high-sensitively and continuously measuresoot represented is the soot detector comprising an electric chargeimparting part that imparts electric charge to soot and an electriccharge measuring part that measures a quantity of electric charge ofsoot.

As the SOF measuring system suitable for soot measurement in accordancewith this invention represented is the SOF measuring system comprising abifurcated part that bifurcates the introduced exhaust gas, a particlecomponent removing line that sets one of the bifurcated exhaust gas at ameasurement reference temperature for SOF measurement and removesparticle component in the exhaust gas kept at the measurement referencetemperature, a passing line that passes other bifurcated exhaust gas,and hydrocarbon concentration detectors each of which continuouslydetects hydrocarbon concentration in the exhaust gas sent out from theparticle component removing line and the passing line respectively, andthe SOF measuring system is so arranged that the SOF concentration inthe exhaust gas can be calculated based on a difference between thehydrocarbon concentration detected by one of the hydrocarbonconcentration detectors and the hydrocarbon concentration detected bythe other hydrocarbon concentration detector. The term here “particlecomponent” is mainly hydrocarbon particle liquefied or solidified ingas.

The hydrocarbon concentration detector is especially preferably ahydrogen flame ionization detector. In case that the SOF measuringsystem is arranged by the use of the hydrogen flame ionization detector,soot is detected in a spike-like peak state, if an output from thehydrogen flame ionization detector locating at a side of a passing lineis graphed. As a result, it is possible, for example, to verify theconcentration of soot measured by the soot measuring system.

In order to measure the concentration of soot in the exhaust gas bymaking use of the exhaust gas analyzer in accordance with thisinvention, it is preferable that the hydrocarbon concentration of thediluted standard gas is measured by the SOF measuring system, thedilution ratio of the diluter is calculated based on a ratio of thehydrocarbon concentration of the diluted standard gas to the hydrocarbonconcentration of the standard gas prior to dilution, a correlationbetween the dilution ratio and an operated amount is obtained based onthe operated amount of the dilution ratio adjusting device at that time,the dilution ratio is adjusted so as to become a desired value at a timeof soot measurement by operating the dilution ratio adjusting device bythe operated amount obtained from the correlation, or the dilution ratiois obtained based on the operated amount of the dilution ratio adjustingdevice set at a time of soot measurement and the correlation, and theconcentration of soot in the exhaust gas is calculated based on thedilution ratio and the measured result by the soot detector.

In accordance with this invention, it is possible to obtain the dilutionratio of the exhaust gas necessary for measuring the concentration ofsoot accurately just with the simple flow path by making use of the SOFmeasuring system together with the soot measuring system in case ofmeasuring the particulate matter.

Next, regarding the problem (2), the exhaust gas analyzer in accordancewith the present claimed invention is so arranged that a soot measuringsystem that can measure soot is connected with an exhaust gas linethrough which a part or all of exhaust gas discharged from an internalcombustion engine flows, and characterized by that the soot measuringsystem comprises a diluter that dilutes the exhaust gas with diluent gasand extrudes it, a dilution ratio adjusting device that can adjust thedilution ratio of the diluter, and a soot detector that detects soot inthe exhaust gas diluted by the diluter, wherein the diluter is soarranged that a narrow part whose flow path diameter is narrowed and adiffusible part whose flow path diameter is extended are seriallyarranged on an internal main path through which the diluent gas passesso as to form a negative-pressure area that is negative-pressuredbecause the diluent gas is accelerated, and the diluter sucks theexhaust gas through a communicating path communicating with thenegative-pressure area, mixes the exhaust gas with the diluent gas andthen extrudes it, and the dilution ratio adjusting device changes a flowamount of the diluent gas introduced into the diluter within a rangewhere a flow amount of the exhaust gas sucked by the diluter is keptgenerally constant by a predetermined operation from outside.

In accordance with this arrangement, since the dilution ratio can beeasily adjusted by the use of the dilution system so that concentrationof varieties of exhaust gas becomes appropriate for the soot detection,it is possible to measure the concentration of soot by the use of thehigh-precision soot detector. In addition, a possibility that the fluidpath is clogged with soot can be avoided as much as possible because ofa merit of the diluter of this type, namely the simple fluid path.Furthermore, the diluted exhaust gas can be sent out to the sootdetector in a stable state without fail because of a merit that thediluter has no pulsation that prevents the accurate concentrationmeasurement.

As a soot detector whose effect can especially be significant when thepresent claimed invention is applied represented is the soot detectorcomprising an electric charge imparting part that imparts electriccharge to soot and an electric charge measuring part that measureselectric charge of soot.

In order to simultaneously detect SOF as well as soot contained in theexhaust gas, it is preferable that an SOF measuring system that canmeasure concentration of SOF is further connected with the exhaust gasline. As the SOF measuring system in this case, it is preferable thatthe SOF measuring system comprises a bifurcated part that bifurcates theintroduced exhaust gas, a particle component removing line that sets oneof the bifurcated exhaust gas at a measurement reference temperature andremoves particle component in the exhaust gas kept at the measurementreference temperature, a passing line that passes other bifurcatedexhaust gas, and hydrocarbon concentration detectors each of whichcontinuously detects hydrocarbon concentration in the exhaust gas sentout from the particle component removing line and the passing linerespectively, and the SOF is so arranged that the SOF concentration inthe exhaust gas can be calculated based on a difference between thehydrocarbon concentration detected by one of the hydrocarbonconcentration detectors and the hydrocarbon concentration detected bythe other hydrocarbon concentration detector.

The term here “particle component” is mainly hydrocarbon particleliquefied or solidified in gas.

The hydrocarbon concentration detector is especially preferably ahydrogen flame ionization detector. In case that the SOF measuringsystem is arranged by the use of the hydrogen flame ionization detector,soot is detected in a spike-like peak state, if an output from thehydrogen flame ionization detector locating at a side of a passing lineis graphed. As a result, it is possible, for example, to verify theconcentration of soot measured by the soot measuring system and to setup a standard of an optimum dilution ratio based on its result.

Since an object to be measured by the soot detector is the dilutedexhaust gas, it is necessary to grasp a dilution ratio finally in orderto measure the concentration of soot in the exhaust gas.

Then in order to make it possible to obtain the dilution ratioaccurately with a simple arrangement by making use of the SOF measuringsystem it is preferable that the diluter is arranged to selectivelyintroduce either one of the exhaust gas and standard gas whosehydrocarbon concentration is known so that the selected gas can bediluted, the SOF measuring system can measure concentration ofhydrocarbon in the standard gas diluted by the diluter with anarrangement that the SOF measuring system can be connected with thediluter, and the dilution ratio of the diluter at this state can becalculated based on the concentration of hydrocarbon in the standard gasafter dilution when the dilution ratio adjusting device is operated by acertain amount.

In addition, the present claimed invention can be applied broadly as agas mixing system including diluting gas without being limited to thesoot measurement. More specifically, the mixing system in accordancewith the present claimed invention comprises a mixer where a narrow partwhose flow path diameter is narrowed and a diffusible part whose flowpath diameter is extended are serially arranged on an internal main paththrough which mixing gas as being gas to mix passes so as to form anegative-pressure area that is negative-pressured because the mixing gasis accelerated, and the mixing system sucks mixed gas as being gas to bemixed through a communicating path communicating with thenegative-pressure area, mixes the mixed gas with the mixing gas and thenextrudes it, and a mixing ratio adjusting device that changes a flowamount of the mixing gas introduced into the mixer within a range wherea flow amount of the mixed gas sucked by the mixer is kept generallyconstant by a predetermined operation from outside.

In accordance with the mixing system, it is possible to adjust themixing ratio easily by the use of the mixing ratio adjusting device inaddition to mix the mixed gas with the mixing gas in a stable statebecause the flow path of the mixer is simple and free from pulsation.

In order to make this effect further more remarkably, it is preferableto further comprise a gas component detector that is connected with agas extruding port of the mixer and that can continuously detect acomponent of the mixed gas.

As a concrete embodiment of the mixing ratio adjusting devicerepresented is the mixing ratio adjusting device comprising a pressureregulator arranged on a mixing gas line through which the mixing gasflows, and a flow rate of the mixing gas introduced into the mixer fromthe mixing gas line is changed by an operation to adjust the pressure ofthe pressure regulator.

In case of using this mixing system as the diluting system, the diluentgas corresponds to the mixing gas, the exhaust gas corresponds to themixed gas, the diluter corresponds to the mixer, the dilution ratioadjusting device corresponds to the mixing ratio adjusting device, andthe gas component detector corresponds to the soot detector.

As mentioned above, in accordance with this invention, it is possible tochange and adjust the dilution (mixing) ratio easily and to stabilizequality of the diluted (mixed) gas without pulsation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall fluid circuit diagram of an exhaust gas analyzer inaccordance with one embodiment of the present claimed invention.

FIG. 2 is a cross-sectional view showing an internal structure of adiluter in accordance with this embodiment.

FIG. 3 is a cross-sectional view of an enlarged portion mainly showing anozzle, a diffuser and an orifice of the diluter in accordance with thisembodiment.

FIG. 4 is a graph showing a characteristic of the diluter in accordancewith this embodiment.

FIG. 5 is a pattern diagram of a soot detector in accordance with thisembodiment.

FIG. 6 is a flow chart showing a method for measuring soot by making useof the exhaust gas analyzer in accordance with this embodiment.

FIG. 7 is a flow chart showing a method for measuring soot by making useof the exhaust gas analyzer in accordance with this embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An exhaust gas analyzer in accordance with one embodiment of the presentclaimed invention will be described in detail with reference to theaccompanying drawings.

(1) Overall Configuration of the Exhaust Gas Analyzer

The exhaust gas analyzer 1 in accordance with this embodiment is tomeasure mass concentration of SOF (soluble organic fraction) and sootcontained in exhaust gas of a diesel engine (not shown in drawings) asbeing an internal combustion engine and, as shown in FIG. 1, comprisesan SOF measuring system 2 that can continuously measure massconcentration of SOF and a soot measuring system 3 that can continuouslymeasure mass concentration of soot, each of which is connected inparallel with an exhaust gas line (not shown in drawings) to which apart or all of the exhaust gas is discharged from the diesel engine.

(2) SOF Measuring System

First, the SOF measuring 2 system will be explained.

The SOF measuring system 2 comprises, as shown in FIG. 1, a bifurcatedpart 21 that bifurcates the exhaust gas introduced from the exhaust gasline, a passing line 22 and a particle composition removal line 23 intoeach of which the exhaust gas bifurcated by the bifurcated part 21 isintroduced respectively, and hydrogen flame ionization detectors 24 a,24 b each of which is connected with each of the passing line 22 and theparticle composition removal line 23 respectively through pumps Pa, Pb.

The bifurcated part 21 is formed by making use of a manifold block 25having a fluid path bifurcating internally, and the exhaust gas line isconnected with a gas introducing port PT1 as being an introducing portof the manifold block 25 through a temperature control pipe L such as ahot hose pipe heated to a predetermined temperature (approximate 191°C.) or a particulate matter removal filter F. A temperature controllerH1 such as a heater that can control temperature is mounted on themanifold block 25 and the manifold 25 is kept at, for example, thepredetermined temperature (approximate 191° C.).

The particle composition removal line 23 sets a temperature of theexhaust gas flowing internally at 47° C.±5° C. as a measurement standardtemperature ordained by the 2007 EPA regulation, removes hydrocarbon(SOF) that liquidized or solidified at this temperature and extrudes theexhaust gas after the hydrocarbon is removed to the hydrogen flameionization detector 24 b.

More concretely, the particle composition removal line 23 is connectedwith the gas introducing port PT1 through the manifold block 25, andcomprises a first temperature control pipe L1 heated to the measurementstandard temperature, a filter F1 connected with a terminal of the firsttemperature control pipe L1, and a second temperature control pipe L2that introduces the gas passing the filter F1 into the hydrogen flameionization detector 24 b. The second temperature control pipe L2 isheated to, for example, the predetermined temperature (approximate 191°C.).

The passing line 22 extrudes the exhaust gas heated to the predeterminedtemperature higher than the measurement standard temperature, moreconcretely 191° C. directly to the hydrogen flame ionization detector 24a, and comprises a third temperature control pipe L3 connected with thegas introducing port PT1 through the manifold block 25. The thirdtemperature control pipe L3 is heated to the predetermined temperature(approximate 191° C.) and connected with the hydrogen flame ionizationdetector 24 a.

The hydrogen flame ionization detector 24 a, 24 b is to continuously andreal-time detect mass concentration of hydrocarbon contained in samplegas (the exhaust gas in the above case) by flowing the sample gas. Thehydrogen flame ionization detector 24 a, 24 b ionizes the hydrocarbon inthe sample gas by passing the sample gas (the exhaust gas in this case)through the hydrogen flame and detects and outputs its ionic current. Anoutput value of the detecting signal shows the mass concentration ofhydrocarbon.

In accordance with this arrangement, since a base line value of thedetecting signal by the hydrogen flame ionization detector 24 aconnected with the passing line 22 shows the mass concentration ofhydrocarbon in a vaporized condition at the predetermined temperature(191° C.) and a base line value of the detecting signal by the hydrogenflame ionization detector 24 b connected with the particle compositionremoval line 23 shows mass concentration of vaporized hydrocarbon at themeasurement standard temperature (47° C.±5° C.) is possible to measurethe mass concentration of hydrocarbon condensed from the gaseous body tothe liquid body or to the solid body between (47° C.±5° C.) and 191° C.,namely the mass concentration of SOF in the exhaust gas by obtaining adifference between the values of the detecting signal by each of thehydrogen flame ionization detectors 24 a, 24 b.

In this embodiment, an information processing unit, not shown indrawings, receives the hydrocarbon detecting signals from the hydrogenflame ionization detectors 24 a, 24 b respectively, and calculates themass concentration of SOF by obtaining a difference between the valuesshown by the hydrocarbon detecting signals and outputs the massconcentration of SOF to a display or the like.

(3) Soot Measuring System

Next, the soot measuring system 3 will be explained.

The soot measuring system 3 comprises, as shown in FIG. 1, a dilutingsystem 4A that dilutes the exhaust gas with air as being diluent gas andsends it out and a soot detector 5 that detects mass concentration ofsoot in the diluted gas.

The diluting system 4A comprises, as shown in FIG. 1 through FIG. 3, adiluter 4 and a pressure regulator 7 as being a dilution ratio adjustingdevice.

The diluter 4 is an ejector-type, whose detail is shown in FIG. 2 andFIG. 3, wherein a nozzle 42 as being a narrow part whose flow pathdiameter is narrowed along a direction of a gas flow and a diffuser 43as being a diffusible part whose flow path diameter is extended arearranged in this order serially on an internal main path 41 throughwhich the diluent gas flows so as to form a negative-pressure area 4Sthat is negative-pressurized because the diluent gas is accelerated, andthe sample gas is sucked through a communicating path 44 communicatingto the negative-pressure area 4S, mixed with the diluent gas and thensent out. The nozzle is used as the narrow part and the diffuser is usedas the diffusible part in this embodiment, however, various substitutessuch as an orifice or a venturi tube may be used.

More specifically, the diluter 4 mainly comprises a piping block body 4a having the communicating path 44 communicating to the main path 41 andthe negative-pressure area 4S, a nozzle member 42 a that forms thenozzle 42 by being inserted into the main path 41, a diffuser member 43a that forms the diffuser 43 by being inserted into the main path 41, aninlet port PT2 as being an inlet of the main path 41, an outlet port PT3as being an outlet of the main path 41, a sample gas introducing portPT4 as being an inlet of the communicating path 44, and joints forcoupling C2, C3, C4 arranged on the inlet port PT2, the outlet port PT3and the sample gas introducing port PT4 respectively.

A temperature controller H2 such as a heater that can adjust temperatureis mounted on the piping block body 4 a and the diluter 4 is heated tothe predetermined temperature (approximate 191° C.). This is to volatizeSOF or the like (especially SOF that attaches to soot) contained in theexhaust gas so as to prevent an adverse effect on soot measurement by asoot detector 5, to be described later. Since the soot detector 5 is atype incapable of introducing high-temperature gas, the temperature ofthe diluted exhaust gas is lowered during passing through a piping L4from the outlet port PT3 of the diluter 4 to the soot detector 5. SOFthat has once vaporized will never be separated out again as a particlethat has influence on the measurement because SOF is diluted even thoughthe temperature of the diluted exhaust gas is lowered.

In addition, a portion to be directly connected with the inlet port PT2of a diluent gas line 6 is heated to the predetermined temperature(approximate 191° C.) by the use of a fourth temperature control pipe L5so as to stabilize air flow to be supplied.

Furthermore, as shown in FIG. 1, the diluent gas line 6 through whichthe diluent gas passes is connected with the inlet port PT2 so as tointroduce air as being the diluent gas, and the exhaust gas line isconnected with the sample gas introducing port PT4. In addition, thesoot detector 5 is connected with the outlet port PT3 through the pipingL4 so that the diluted gas can be sent out to the soot detector 5.

In addition, an orifice ring 44 a as being a flow limit member isexchangeably mounted, as shown in FIG. 3, at least on the communicatingpath 44 of the diluter 4 locating in a former stage.

A diluent gas source (not shown in drawings) such as a compressor or asteel bottle is connected with a leading end of the diluent gas line 6and the pressure regulator 7 as being a dilution ratio adjusting deviceis arranged on the diluent gas line 6 so that the dilution ratio can beadjusted by controlling pressure of the air flowing into the inlet portPT2.

The pressure regulator 7 is arranged on the diluent gas line 6 andcontrols the pressure of the air flowing into the inlet port PT2 of thediluter 4 so as to control its air flow.

However, generally it is not possible for a diluter of ejector-type tochange a dilution ratio arbitrarily. This is based on a fact that thepressure in the negative-area 4S decreases if a lot of diluent gas (forexample, air) is flowed and therefore the flow volume of the sample gasincreases by just this much. As a result of this, the dilution ratiodoes not fluctuate significantly.

Then in this embodiment, as shown in FIG. 4, an operation range of thepressure regulator 7, namely a pressure adjustable range is restrictedto a range where the sucked flow of the sample gas in the diluter 4 iskept generally constant due to pressure adjustment even if the flow ofthe diluent gas introduced into the diluter 4 changes. More concretely,a range of the air pressure is between 300 kPa through 500 kPa. It is amatter of course that this range depends on a shape or a size of thenozzle or the diffuser, or a diameter of the orifice, however, it is notuntil this range is used that the pressure regulator 7 acts as thedilution ratio adjusting device and the dilution ratio can be changed bythe operation of the pressure setting.

In this embodiment, in order to broaden a range to adjust the dilutionratio, the diluters 4 are connected serially in plural (two) stages.More specifically, the outlet port PT3 of the diluter 4 locating in aformer stage is connected with the sample gas introducing port PT4 ofthe diluter 4 locating in a later stage so that dilution can beconducted in plural stages. As a result, the dilution ratio can bechanged in compliance with an order by selecting which outlet port PT3is to be used.

In accordance with the diluting system 4A of this embodiment, it ispossible to adjust the dilution ratio easily so that the high-precisionsoot detector can maintain appropriate mass concentration of soot toexert its performance fully with maintaining merits of the diluter 4,namely merits wherein the flow path is prevented from being clogged withsoot and free from pulsation.

The soot detector 5 comprises, whose pattern diagram is shown in FIG. 5,an electric charge imparting part 51 that imparts electric charge tosoot contained in the sample gas and an electric charge measuring part52 that measures electric charge of soot, and continuously and real-timemeasures soot contained in the diluted exhaust gas introduced as thesample gas.

The electric charge imparting part 51 is arranged on the flow path 53 ofthe introduced diluted exhaust gas, and comprises a positive electrode511 and a negative electrode 512, wherein a potential difference betweenthe positive electrode 511 and the negative electrode 512 is, forexample, several thousands volt (5000 through 7000 volt). Coronadischarge is generated between the positive electrode 511 and thenegative electrode 512 due to its potential difference and the sootparticle in the diluted exhaust gas is charged in proportion to itssurface area as a result that the diluted exhaust gas passes between thepositive electrode 511 and the negative electrode 512. As an example isshown in FIG. 5, the positive electrode 511 is in a thin shape of a pintype locating at a center of the flow path 53, and the negativeelectrode 512 is a cylindrical cancellous member arranged to surroundthe positive electrode 511. The electric charge imparting part 51 mayhave other arrangement, for example, the electric charge is imparted byirradiating ultraviolet rays.

The electric charge measuring part 52 comprises a capturing member 521such as a metal plate arranged downstream of the electric chargeimparting part 51 in the flow path 53 and a current detector 522 thatmeasures a value of the current that soot captured by the capturingmember 521 flows and outputs soot detecting signal showing its value.The value of the soot detecting signal expresses a surface area of thesoot particles because the quantity of electric charge is proportionalto a surface area of the soot particles. In addition, since there is apredetermined relational expression between the surface area of the sootparticles and the mass of the soot particles, the mass of the sootparticles, consequently concentration of soot in the diluted exhaust gascan be calculated from the value of the detecting signal.

However, what required finally is concentration of soot in the exhaustgas prior to dilution, and it is necessary to grasp the dilution ratioby the diluter 4 in addition to measured data of the concentration ofsoot in the diluted exhaust gas in order to measure the concentration ofsoot in the exhaust gas prior to dilution.

Then in this embodiment, as shown in FIG. 1, it is so arranged that astandard gas line 8 through which standard gas (for example, aircontaining C₃H₈) whose hydrocarbon concentration is known flows and theexhaust gas line can be switched to be connected with the sample gasintroducing port PT4 of the diluter 4, and the outlet port PT3 of thediluter 4 and the exhaust gas line can be switched to be connected withthe gas introducing port PT1 of the SOF measuring system 2.

More specifically, connection of the standard gas line 8 and the exhaustgas line with the sample gas introducing port PT4 can be switched byproviding a switch valve V2 on the piping L6 of the standard gas line 8to the sample gas introducing port PT4 of the diluter 4. A standard gassource (such as a steel bottle) is connected with an inlet of thestandard gas line 8, a pressure regulator 81 is arranged so that linepressure of downstream the pressure regulator 81 can be kept at aconstant value and a flow instrument 82 is arranged so that flow of thestandard gas introduced into the sample gas introducing port PT4 can bemonitored.

A switch valve V3 is arranged on a connection piping L7 from the outletport PT3 of the diluter 4 with the gas introducing port PT1 of the SOFmeasuring system 2, a switch valve V4 is arranged on a connection pipeof the exhaust gas line with the gas introducing port PT1, and eitherone of the outlet port PT3 of the diluter 4 and the exhaust gas line canbe switched to be connected with the gas introducing port PT1 byalternative selection of the switch valves V3, V4.

In accordance with this arrangement, it is possible for either one ofthe hydrogen flame ionization detector 24 a and the hydrogen flameionization detector 24 b to measure the hydrocarbon concentration of thediluted standard gas by making the standard gas diluted by the diluter 4flow into the SOF measuring system 2 with an operation of the switchvalves V3, V4. Then the dilution ratio of the diluter 4 at that time canbe obtained based on the measured hydrocarbon concentration of thediluted standard gas and the known hydrocarbon concentration of thestandard gas, and then the concentration of soot in the exhaust gas canbe calculated based on the dilution ratio and the concentration of sootin the diluted exhaust gas.

Furthermore, in this embodiment, an information processing unit, notshown in drawings, receives the soot detecting signal and thehydrocarbon detecting signal output by the hydrogen flame ionizationdetector 24 a (24 b) at a time when the diluted standard gas is flowed,and outputs the concentration of soot automatically calculated based onthese values and the previously memorized known concentration data ofthe standard gas to a display or the like. In addition, each of theswitch valves V2, V3, V4 is of an electromagnetic drive type and drivento open or close by a valve driving signal output by the informationprocessing unit.

(4) Usage of the Exhaust Gas Analyzer

Next, one example of a method for measuring the concentration of soot bymaking use of the exhaust gas analyzer 1 will be concretely explained. Acase that the information processing unit automatically measures theconcentration of soot in accordance with a program will be explainedwith reference to FIG. 6 and FIG. 7.

(Drawing Up an Analytical Curve)

First, the standard gas is introduced into the SOF measuring system 2through the diluter 4 by operating each of the switch valves V2, V3, V4to open or close with the valve driving signal output to each of theswitch valves V2, V3, V4 (FIG. 6: Step S1).

The air introduced into the diluter 4 is kept at a predeterminedpressure by giving a driving signal to the pressure regulator 7 (StepS2).

With this state kept, the hydrocarbon concentration in the dilutedstandard gas is measured by the hydrogen flame ionization detector 24 a(24 b) (Step S3).

The dilution ratio of the diluter 4 is calculated based on a ratio ofthe hydrocarbon concentration in the diluted standard gas to thehydrocarbon concentration in the standard gas prior to dilution (StepS4), and the dilution ratio and the air pressure are recorded in pairs(Step S5).

Next, a pressure of air introduced into the diluter 4 is changed to setat a different value by changing a value of the driving signal to thepressure regulator 7 (Step S6) and the step S3 through the step S6 arerepeated at plural times (n times) (Step S7, S8).

An analytical curve between the pressure and the dilution ratio(relative relationship) is drawn up based on a relationship betweenvalues of the pressure measured at plural points and the dilution ratioand then stored in a predetermined area of the memory (Step S9).

(Soot Concentration Measurement)

First, the exhaust gas is introduced into the soot measuring system 3 byoperating each of the switch valves V2, V3, V4 to open or close (FIG. 7:Step S10)

Because the concentration of soot in the exhaust gas is unknown, thevalue of the driving signal to the pressure regulator 7 is changed withreference to a value of the soot detecting signal from the soot detector5 so that the pressure of the diluent gas line 6 is set to be suitablefor the soot concentration measurement (Step S11, S12).

The dilution ratio at that time is calculated based on the set value ofthe air pressure and the analytical curve (Step S13).

The soot concentration in the diluted exhaust gas is obtained byapplying a predetermined relational expression stored in the memory tothe value of the soot detecting signal (Step S14).

Finally, the concentration of soot in the exhaust gas is calculatedbased on the concentration of soot in the diluted exhaust gas and thedilution ratio (Step S15).

The method for measuring the concentration of soot is mentioned above,and may be others, for example, the analytical curve is not drawn up,the dilution ratio at the set value of the pressure of the diluent gasat that time is calculated by the use of the standard gas every time theconcentration of soot is measured and the concentration of soot iscalculated based on the dilution ratio.

In addition, all of the above-mentioned actions may be operated manuallyby an operator, or a part of them may be automatically operated andother may be operated manually.

As a result, in accordance with the exhaust gas analyzer 1, it ispossible to obtain the dilution ratio of the diluter 4 at a time of sootmeasurement by the use of the standard gas at a time prior to or aftersoot measurement and to calculate the concentration of soot in theexhaust gas prior to dilution based on the obtained dilution ratio andthe concentration of soot in the diluted exhaust gas detected by thesoot detector with a simple arrangement of a flow path wherein thepiping is bifurcated from the diluter 4 to be connected with theexisting SOF measuring system 2, the piping to connect the standard gassource is connected with the diluter 4, or the switch valves V2, V3, V4are arranged on the piping.

In addition, since the dilution ratio can be easily adjusted by the useof the dilution system 4A so that concentration of varieties of exhaustgas becomes appropriate for the soot detection, it is possible tomeasure the concentration of soot by the use of the high-precision sootdetector 5. In addition, a possibility that the fluid path is cloggedwith soot can be avoided as much as possible because of a merit of thediluter 4 of this type, namely the simple fluid path. Furthermore, thediluted exhaust gas can be sent out to the soot detector in a stablestate without fail because of a merit that the diluter 4 has nopulsation that prevents the accurate concentration measurement.

Furthermore, since the hydrogen flame ionization detector 24 a, 24 bdetects soot in a spike-like peak state, it is possible, for example, toverify the concentration of soot measured by the soot measuring systemand to set up a standard of an optimum dilution ratio based on itsresult.

The present claimed invention is not limited to the above-mentionedembodiment. For example, the hydrocarbon detector or the soot detectormay utilize other principle, or the exhaust gas line may introduceexhaust gas diluted by a full tunnel.

The diluter may have an arrangement of one stage, or of three or morestages. The diluter is not limited to be of the ejector type, and may beof other type such as a rotary pump type.

Furthermore, the dilution ratio adjusting device may utilize not onlythe pressure regulator but also a flow adjusting valve such as a valve.

In addition, this diluting system may be used for diluting or mixingother gas. Other arrangement may be variously modified without departingfrom a spirit of the present claimed invention such as the switch valvemay be a three-way valve.

As mentioned above, the present claimed invention makes it possible tocontinuously and high-precisely measure the concentration of soot inexhaust gas with a simple and compact arrangement, which facilitatesresearch and development of an internal combustion engine such as anautomobile. In addition, it is possible to change and adjust thedilution (mixing) ratio easily as well as to stabilize quality of thediluted (mixed) gas free from pulsation. As a result, the presentclaimed invention can be broadly applied to a usage such as gascontinuous measurement.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

1. A mixing system comprising: a mixer wherein a narrow part whose flowpath diameter is narrowed and a diffusible part whose flow path diameteris extended are serially arranged on an internal main path through whichmixing gas passes so as to form a negative-pressure area that isnegative-pressured because the mixing gas is accelerated and that sucksmixed gas through a communicating path communicating with thenegative-pressure area and mixes the mixed gas with the mixing gas andthen extrudes it; and a mixing ratio adjusting device that changes aflow amount of the mixing gas introduced into the mixer within a rangewhere a flow amount of the mixed gas sucked by the mixer is keptgenerally constant by a predetermined operation from outside.
 2. Themixing system of claim 1, wherein a gas component detector is connectedwith a gas extruding port of the mixer and can continuously detect acomponent of the mixed gas.
 3. The mixing system of claim 1, wherein themixing ratio adjusting device comprises a pressure regulator arranged ona mixing gas line through which the mixing gas flows, a flow rate of themixing gas introduced into the mixer from the mixing gas line is changedby an operation to adjust pressure of the pressure regulator.